Support viewing PDFs & images on the dataset landing pages

[robyngit]

The first initial iteration of the "data table previews" feature will be released soon with support for viewing csv & tsv files as tables directly from the dataset landing pages (see https://github.com/NCEAS/metacatui/issues/1758).

We should add to this feature by also allowing users to view PDFs and images directly from the dataset landing pages. This would be useful for viewing data files that are in PDF format, or for viewing images that are in common image formats like .png, .jpg, .gif, etc.